NAME¶
swapon,
swapoff,
swapctl
—
specify devices for paging and swapping
SYNOPSIS¶
swapctl |
[-AghklmsU]
[-a file ... |
-d file ...] |
DESCRIPTION¶
The
swapon,
swapoff and
swapctl utilities are used to control swap devices in the
system. At boot time all swap entries in
/etc/fstab are
added automatically when the system goes multi-user. Swap devices use a fixed
interleave; the maximum number of devices is specified by the kernel
configuration option
NSWAPDEV
, which is typically set
to 4. There is no priority mechanism.
The
swapon utility adds the specified swap devices to the
system. If the
-a option is used, all swap devices in
/etc/fstab will be added, unless their “noauto”
option is also set. If the
-q option is used informational
messages will not be written to standard output when a swap device is added.
The
swapoff utility removes the specified swap devices from
the system. If the
-a option is used, all swap devices in
/etc/fstab will be removed, unless their
“noauto” option is also set. If the
-q option is
used informational messages will not be written to standard output when a swap
device is removed. Note that
swapoff will fail and refuse to
remove a swap device if there is insufficient VM (memory + remaining swap
devices) to run the system. The
swapoff utility must move
swapped pages out of the device being removed which could lead to high system
loads for a period of time, depending on how much data has been swapped out to
that device.
The
swapctl utility exists primarily for those familiar with
other
BSDs and may be used to add, remove, or list
swap devices. Note that the
-a option is used differently in
swapctl and indicates that a specific list of devices should
be added. The
-d option indicates that a specific list
should be removed. The
-A and
-U options
to
swapctl operate on all swap entries in
/etc/fstab which do not have their “noauto”
option set.
Swap information can be generated using the
swapinfo(8)
utility,
pstat -s, or
swapctl -l. The
swapctl
utility has the following options for listing swap:
- -h
- Output values in human-readable form.
- -g
- Output values in gigabytes.
- -k
- Output values in kilobytes.
- -m
- Output values in megabytes.
- -l
- List the devices making up system swap.
- -s
- Print a summary line for system swap.
The
BLOCKSIZE
environment variable is used if not
specifically overridden. 512 byte blocks are used by default.
FILES¶
- /dev/{ad,da}?s?b
- standard paging devices
- /dev/md?
- memory disk devices
- /etc/fstab
- ASCII file system description table
DIAGNOSTICS¶
These utilities may fail for the reasons described in
swapon(2).
SEE ALSO¶
swapon(2),
fstab(5),
init(8),
mdconfig(8),
pstat(8),
rc(8)
HISTORY¶
The
swapon utility appeared in
4.0BSD.
The
swapoff and
swapctl utilities appeared
in
FreeBSD 5.1.